The goal of this research is to describe the mariner family transposons of diverse mammals, evaluate their molecular evolutions within mammals, understand their origins, and characterize their contributions both negative and positive to mammalian genomes. Two mariner family transposons, each with hundreds of copies, have recently been described in the human genome. We have evidence of two more in other primates and three others in other mammals. We propose to continue to screen mammals for mariners and to complete characterization of these transposons. They will be placed in the context of our extensive databases of mariner transposons from other animals to understand their origins and molecular evolution. The two human mariners are ancient components of our genome, and the timing of their acquisition will be refined by examining multiple orthologous copies in the same insertion positions within genes from diverse primates. Similar approaches will be used to evaluate the origins of two distantly related Tigger transposons in the human genome. We have discovered that a particular copy of one of the human mariners has been remarkably conserved over the past +/- 50 Myr in the human genome, apparently because its transposase gene has become an exon of a chimeric gene we call SETMAR. The other half of this SETMAR gene encodes a SET domain shared with a variety of proteins that affect chromatin structure. We will evaluate the evolutionary origins of this novel SETMAR gene and the contribution of the transposase domain to its function. This work will greatly expand our understanding of the evolutionary dynamics of mariner family transposons, currently the best understood family of DNA-mediated transposons in eukaryotes, particularly with respect to the occurrence of trans-phyla horizontal transfers. It will also reveal how occasionally particular copies of transposons can become integral parts of their host genetic complements.